Characterisation of target nucleic acids is highly important for several reasons relating to confirmation of the presence or absence of a gene in a sample, confirmation of part or all of a nucleic acid sequence, and screening for the presence of known and unknown disease causing mutations leading to inherited disease and natural variations in DNA. Although there are many known methods for characterising nucleic acid and for the detection of unknown sequence changes, the increasing amount of new genetic information being generated makes it important to develop new, better and faster methods for characterisation of nucleic acids.
WO 97/03210 discloses the use of a DNA-glycosylase enzyme, which recognises a modified base, for the direct detection of known and unknown mutations in a target nucleic acid sample. The method typically involves amplifying a target nucleic acid sample using a combination of normal DNA precursor nucleotides and one or more modified precursor nucleotide(s) where the modified precursor nucleotide replaces one of the normal precursor nucleotides which is a substrate for a DNA glycosylase. Following excision of the modified base by the glycosylase, the resulting abasic site is cleaved and the products of the cleavage are analysed. This method allows detection of mutations at candidate loci. However, the method of WO 97/03210 has certain limitations. For example, with this method it is not possible to detect sequence differences between nucleic acid molecules without detecting sequence similarities and thus multiple samples cannot be combined for simultaneous analysis.